This proposal is directed toward the isolation of genes from Streptococcus mutans which may play significant roles in the cariogenicity of the organism. The genes for the glucosyltransferase activity from S. mutans GS5 will be isolated in a streptococcal cloning system utilizing Streptococcus milleri as a host. Clones exhibiting glucosyltransferase activity will be characterized both physically and enzymatically to determine whether one or two enzymes are involved in insoluble glucan formation. The chimeric plasmids isolated from these clones will also be utilized to transfer mutants of strain GS5 which are defective in glucan synthesis. Such an approach will be useful in further characterizing the mechanism of adherent glucan synthesis by S. mutans. Since S. mutans GS5 also synthesizes a bacteriocin (mutacin) which may play a role in colonizing tooth surfaces, the gene for the mutacin will be isolated in the S. milleri cloning system. The isolation of a clone carrying multiple copies of the mutacin gene will be exploited to purify the inhibitor. Utilizing purified mutacin preparations, the mechanism of action of the inhibitor will be examined both with intact indicator cells and cell-free preparations. The nature of the natural immunity of strain GS5 to its own mutacin will also be investigated following the isolation of mutants altered in immunity. One of these mutants will also be utilized to clone the gene for a putative immunity protein. Finally, the effects of human oral host factors (serum, saliva) as well as other oral, plaque organisms on the action of the mutacin will be assessed in vitro with a model plaque system.